Thermally cleavable, soluble pigment derivatives (sometimes also called latent pigments) have recently gained importance. It has become known that they can be used advantageously not only in expensive state-of-the-art technologies, for example colour filters, but also, for example, in wood. As a result, the demands made of production processes for their production in high purity are also increasing.
The production of soluble pigment derivatives is known from EP 648 817 and WO 98/32802. In those processes, pigments are reacted inter alia with dicarbonates in a solvent, optionally in the presence of a catalyst A number of solvents are disclosed, including also aromatic solvents such as benzene, toluene, xylene, anisole, chlorobenzene and pyridine. Preference is given to the highly polar solvents N,N-dimethylformamide, N-methyl-pyrrolidone or tetrahydrofuran. In the Examples, only N,N-dimethylformamide, N,N-dimethyl-acetamide or tetrahydrofuran are used.
It has been found, however, that that method does not always yield satisfactory results to the desired extent. Some pigments produce inexplicably low yields or can be reacted only partially, with hydroxy or amide groups that are retained impairing the desired solubilisation (high solubility) of the product. Other pigments react better, but the crude soluble pigment derivatives obtained therefrom exhibit unsatisfactory purity or inadequate storage stability, so that complex purification steps are necessary. Still further pigments give rise to unexpected problems on a pilot scale or production scale.
It has now been found that certain pigments can be solubilised with surprisingly better results if the reaction is carried out with a pyrocarbonic acid diester in an aromatic solvent. Both the yield and the purity are markedly higher, and more solubilising groups can be incorporated into the pigment. The method according to the invention is also excellently suitable especially for the production of latent pigments in relatively large amounts (xe2x89xa71 mol).
It is in itself very surprising that a more complete reaction is obtained in, of all things, relatively non-polar solvents in which the pigments and soluble pigment derivatives obtained therefrom are less soluble than in solvents used hitherto.
Accordingly, the invention relates to a method for preparing a compound of the formula A(D)x(E)y (I) by reaction of a compound of the formula A(H)x(H)y with a pyrocarbonic acid diester of the formula 
wherein
x and y are each independently of the other an integer from 0 to 6, but x and y are not simultaneously the number 0,
A is the radical of a chromophore of the quinacridone, anthraquinone, perylene, indigo, quinophthalone, indanthrone, isoindolinone, isoindoline, dioxazine, azo, phthalocyanine or diketopyrrolopyrrole series, which radical is bonded via one or more nitrogen atoms to x groups D and via one or more oxygen atoms to y groups E, the nitrogen atoms and oxygen atoms forming part of the radical A,
each group D or E independently of any other(s) is hydrogen or a group of the formula 
wherein at least one group D or E is not hydrogen, and L is any desired group suitable for solubilisation,
in the presence of a base as catalyst, in which method the reaction takes place in an aromatic or heteroaromatic solvent selected from diphenyl, pyridine, quinoline, pyrrole and benzene unsubstituted or mono- to tri-substituted by C1-C6alkyl, phenyl, benzyl, C1-C6-alkoxy, phenoxy, C1-C24alkylthio, halogen and/or by nitro, and any desired mixtures thereof.
Aromatic solvents are preferred. Special preference is given to benzene that is unsubstituted or mono- to tri-substituted by C1-C24alkyl, C1-C24alkoxy or by halogen, for example toluene, o-xylene, mesitylene or isopropylbenzene. Aromatic mixtures, for example Dowtherm(copyright) A, may also be used.
A is preferably the radical of a chromophore of the monoazo, disazo or phthalocyanine series. A preferably has at least one immediately adjacent or conjugated carbonyl group at each nitrogen atom bonded to x groups D.
Preference is given to the production of soluble pigment derivatives of the formula A(D)x(E)y (I) wherein at least one group D that is other than hydrogen is bonded to the nitrogen atom of a hydrazone or sulfonamide group, or wherein at least one group E that is other than hydrogen is bonded to the oxygen atom of an enol, phenol or naphthol. It is also possible, however, for a plurality, or even all, of the groups D and/or E to be bonded to such nitrogen or oxygen atoms.
In the case of the above-mentioned preferred pigment classes, the complete reaction of all substitutable hydrogen atoms, which is desirable for use in state-of-the-art technologies, has, according to processes used hitherto, surprisingly proved to be impossible when there are more than three substitutable hydrogen atoms. Accordingly, special preference is given to the production of pigment derivatives of the formula A(D)x(E)y (I) containing from 4 to 8, especially from 5 to 8, groups D and E that are not hydrogen. Very special preference is given to the production of pigment derivatives of the formula A(D)x(E)y (I) wherein all of the groups D and E are each a group of the formula 
State-of-the-art technologies are, in addition to colour filters, also applications on anodised aluminium or synthetic ceramics, which are the subject of parallel patent applications.
Soluble pigment derivatives having the following partial structures may be mentioned as examples of a group D that is other than hydrogen and is bonded to the nitrogen atom of a hydrazone or sulfonamide group, or of a group E that is other than hydrogen and is bonded to the oxygen atom of an enol, phenol or naphthol: 
Very special preference is given to the production of soluble pigment derivatives from Colour Index Pigment Yellow 13, Pigment Yellow 93, Pigment Yellow 94, Pigment Yellow 95, Pigment Yellow 128, Pigment Yellow 154, Pigment Red 185 and Pigment Red 222.
Groups suitable for the solubilisation of pigments are known, for example, from the publications mentioned above or from EP 761 772.
L may be any desired group known for the solubilisation of pigments.
L is preferably a group of the formula 
wherein R1, R3 and R2 are each independently of the others C1-C6alkyl,
R4 and R5 are each independently of the other C1-C6alkyl, C1-C6alkyl interrupted by O, S or by N(R12)2, unsubstituted or C1-C6alkyl-, C1-C6alkoxy-, halo-, cyano- or nitro-substituted phenyl or biphenyl,
R6, R7 and R8 are each independently of the others hydrogen or C1-C6alkyl,
R9 is hydrogen, C1-C6alkyl or a group of the formula 
R10 and R11 are each independently of the other hydrogen, C1-C6alkyl, C1-C6alkoxy, halogen, cyano, nitro, N(R12)2, unsubstituted or halo-, cyano-, nitro-, C1-C6alkyl- or C1-C6alkoxy-substituted phenyl,
R12 and R13 are C1-C6alkyl, R14 is hydrogen or C1-C6alkyl and R15 is hydrogen, C1-C6alkyl, unsubstituted or C1-C6alkyl-substituted phenyl,
Q is p,q-C2-C6alkylene that is unsubstituted or mono- or poly-substituted by C1-C6alkoxy, C1-C6alkylthio or by C2-C12dialkylamino, wherein p and q are different position numbers,
X is a hetero atom selected from the group consisting of N, O and S, m being the number 0 when X is O or S and the number 1 when X is N, and
L1 and L2 are each independently of the other [-(pxe2x80x2,qxe2x80x2-C2-C6alkylene)xe2x80x94Zxe2x80x94]nxe2x80x94C1-C6alkyl or C1-C6alkyl unsubstituted or mono- or poly-substituted by C1-C12alkoxy, C1-C12alkylthio, C2-C24dialkylamino, C6-C12aryloxy, C6-C12arylthio, C7-C24alkylarylamino or by C12-C24diarylamino, wherein n is a number from 1 to 1000, pxe2x80x2 and qxe2x80x2 are different position numbers, each Z independently of the other(s) is a hetero atom O, S or C1-C12alkyl-substituted N, and C2--C6alkylene in the repeating units [xe2x80x94C2-C6alkylenexe2x80x94Zxe2x80x94] may be the same or different,
and L1 and L2 may be saturated or unsaturated from 1 to 10 times, may be uninterrupted or interrupted at any desired positions by from 1 to 10 groups selected from the group consisting of xe2x80x94(Cxe2x95x90O)xe2x80x94 and xe2x80x94C6H4xe2x80x94, and may carry no further substituents or from 1 to 10 further substituents selected from the group consisting of halogen, cyano and nitro.
Of special interest are compounds of formula (I) wherein L is C1-C6alkyl, C2-C6alkenyl or 
wherein Q is C2-C4alkylene, and L1 and L2 are [xe2x80x94C2C12alkylenexe2x80x94Zxe2x80x94]nxe2x80x94C1-C12alkyl, or C1-C12alkyl mono- or poly-substituted by C1-C12alkoxy, C1-C12alkylthio or by C2-C24dialkylamino, and m and n are as defined above.
Of very special interest are compounds of formula (I) wherein L is C4-C5alkyl, C3-C6alkenyl or 
wherein Q is C2-C4alkylene, X is O and m is zero, and L2 is [xe2x80x94C2-C12alkylenexe2x80x94Oxe2x80x94]nxe2x80x94C1-C12alkyl, or C1-C12alkyl mono- or poly-substituted by C1-C12alkoxy, especially those compounds wherein xe2x80x94Qxe2x80x94Xxe2x80x94 is a group of the formula xe2x80x94C(CH3)2xe2x80x94CH2xe2x80x94Oxe2x80x94.
Alkyl or alkylene may be straight-chained, branched, monocyclic or polycyclic.
Accordingly, C1-C12alkyl is, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, 2-pentyl, 3-pentyl, 2,2-dimethylpropyl, cyclopentyl, cyclohexyl, n-hexyl, n-octyl, 1,1,3,3tetramethylbutyl, 2-ethylhexyl, nonyl, trimethylcyclohexyl, decyl, menthyl, thujyl, bornyl, 1-adamantyl, 2-adamantyl or dodecyl
When C2-C12alkyl is mono- or poly-unsaturated, it is C2-C12alkenyl, C2-C12alkynyl, C2-C12alkapolyenyl or C2-C12alkapolyynyl, wherein two or more double bonds may optionally be isolated or conjugated, for example vinyl, allyl, 2-propen-2-yl, 2-buten-1-yl, 3-buten-1-yl, 1,3-butadien-2-yl, 2-cyclobuten-1-yl, 2-penten-1-yl, 3-penten-2-yl, 2-methyl-1-buten-3yl, 2-methyl-3-buten-2-yl, 3-methyl-2-buten-1-yl, 1,4-pentadien-3-yl, 2-cyclopenten-1-yl, 2-cyclohexen-1-yl, 3-cyclohexen-1-yl, 2,4cyclohexadien-1-yl, 1-p-menthen-8-yl, 4(10)-thujen-10-yl, 2-norbonen-1-yl, 2,5-norbomadien-1-yl, 7,7-dimethyl-2,4-norcaradien-3-yl or the various hexenyl, octenyl, nonenyl, decenyl or dodecenyl isomers.
C2-C4Alkylene is, for example, 1,2-ethylene, 1,2-propylene, 1,3-propylene, 1,2-butylene, 1,3-butylene, 2,3-butylene, 1,4-butylene or 2-methyl-1,2-propylene. C5-C12Alkylene is, for example, an isomer of pentylene, hexylene, octylene, decylene or dodecylene.
C1-C12Alkoxy is Oxe2x80x94C1-C12alkyl, preferably Oxe2x80x94C1-C4alkyl.
C6-C12Aryloxy is Oxe2x80x94C6-C12aryl, for example phenoxy or naphthyloxy, preferably phenoxy.
C1-C12Alkylthio is Sxe2x80x94C16-C12alkyl, preferably Sxe2x80x94C1-C4alkyl.
C6-C12Arylthio is Sxe2x80x94C6-C12aryl, for example phenylthio or naphthylthio, preferably phenylthio.
C2-C24Dialkylamino is N(alkyl1)(alkyl2) wherein the sum of the carbon atoms in the two groups alkyl1 and alkyl2 is from 2 to 24, preferably N(C1-C4alkyl)-C1-C4alkyl.
C7-C24Alkylarylamino is N(alkyl1)(aryl2) wherein the sum of the carbon atoms in the two groups alkyl and aryl2 is from 7 to 24, for example methylphenylamino, ethylnaphthylamino or butylphenanthrylamino, preferably methylphenylamino or ethylphenylamino.
C12-C24Diarylamino is N(aryl1)(aryl2) wherein the sum of the carbon atoms in the two groups aryl1 and aryl2 is from 12 to 24, for example diphenylamino or phenylnaphthylamino, preferably diphenylamino.
Halogen is chlorine, bromine, fluorine or iodine, preferably fluorine or chlorine, especially chlorine.
n is preferably a number from 1 to 100, especially a number from 2 to 12.
Reaction at a temperature of from 0 to 160xc2x0 C., preferably from 10 to 100xc2x0 C., for from xc2xd to 80 hours, preferably from 2 to 48 hours, is advantageous. The reaction is carried out especially at from 15 to 60xc2x0 C. and at a pressure of from 0.8 to 1.2 bar, especially of approximately 1 bar.
The molar ratio in each case is dependent on the number of radicals D and E to be introduced. The dicarbonate is advantageously used in an equimolar amount or in a slight excess, for example from 1 to 1.5 mol, based on 1 mol of hydrogen atoms to be substituted (i.e. the molar amount of dicarbonate corresponds to 1-1.5xc3x97number of groups D and E in the molecule of the product of the formula A(D)x(E)y (I) that are other than hydrogen, per 1 mol of compound of the formula A(H)x(H)y).
It is advantageous to use from 5 to 50 parts by weight of aromatic or heteroaromatic solvent, based on 1 part by weight of compound of the formula A(H)x(H)y.
Bases suitable as catalyst are, for example, the alkali metals themselves, such as lithium, sodium or potassium and their hydroxides and carbonates, or alkali metal amides, such as lithium, sodium or potassium amide, or alkali metal hydrides, such as lithium, sodium or potassium hydride, or alkaline earth metal or alkali metal alcoholates derived especially from primary, secondary or tertiary aliphatic alcohols having from 1 to 10 carbon atoms, for example lithium, sodium or potassium methoxide, ethoxide, n-propoxide, isopropoxide, n-butoxide, sec-butoxide, tert-butoxide, 2-methyl-2-butoxide, 2-methyl-2-pentoxide, 3-methyl-3-pentoxide, 3-ethyl-3-pentoxide, and also organic aliphatic, aromatic or heterocyclic nitrogen bases, including, for example, diazabicyclooctene, diazabicycloundecene and 4-dimethylaminopyridine, and trialkylamines, for example trimethyl- or triethyl-amine. It is also possible, however, to use a mixture of the mentioned bases.
Preference is given to the organic nitrogen bases, for example diazabicyclooctane, diazabicycloundecene and, especially, 4-dimethylaminopyridine.
The amount of catalyst is advantageously from 0.005 to 2 mol, preferably from 0.02 to 1 mol, especially from 0.1 to 0.4 mol, times the number of groups D and E in the molecule of the product of the formula A(D)x(E)y (I) that are other than hydrogen, based on 1 mol of compound of the formula A(H)x(H)y. Accordingly, for the substitution of a single group there are required from 0.005 to 2 mol of catalyst, while for the substitution of 6 groups there are required from 0.03 to 12 mol of catalyst.
The suitable pyrocarbonic acid diesters of the formula 
can be prepared analogously to generally known methods. Most of the chemicals required therefor are known. Many are commercially available, and all can be prepared by methods known per se.
The product of the formula A(D)x(E)y (I) can be isolated from the reaction mixture by conventional methods. It is preferably precipitated with one or more solvents in which it is sparingly soluble, especially with a saturated hydrocarbon, an aliphatic alcohol, water, or a mixture of a saturated hydrocarbon and an aliphatic alcohol or of an aliphatic alcohol and water, it being especially advantageous for the catalyst to remain in solution. Very special preference is given to precipitation with from 50 to 150% by weight solvent in which the product is sparingly soluble, that amount being based on the compound of the formula A(H)x(H)y.
It may be advantageous to reduce the amount of solvent, before the precipitation, to an amount appropriate to the solubility of the product, for example to from 0.5 to 5 parts by weight aromatic solvent, based on 1 part by weight compound of the formula A(H)x(H)y.